This document discusses attacks on telecommunication networks using vulnerabilities in the Signaling System 7 (SS7) protocol. It describes how stolen mobile devices can be unblocked by exploiting the relationship between the device's IMEI and user's IMSI during the normal IMEI check procedure. The attack involves sending a fake CHECK_IMEI request containing a blacklisted IMEI along with the correct associated IMSI to override the blacklist status. This allows stolen devices to be reactivated without authorization.